The present invention relates to a photographic light-sensitive material and more particularly to a chemically sensitized silver halide photographic light-sensitive material.
Various means of chemical sensitization for increasing the light sensitivity of silver halide photographic emulsions are known. One typical method is known as sulfur sensitization, wherein the light sensitivity of a silver halide photographic emulsion is increased by adding thereto a very small amount of sulfur or a sulfur compound to form silver sulfide, as disclosed, for example, in U.S. Pat. Nos. 2,410,689 and 3,501,313, West German Pat. No. 1,422,869, and Japanese Pat. No. 20533/74.
Also, methods for increasing the light sensitivity of silver halide photographic emulsions by adding thereto a suitable reducing agent or gold compound, known as reduction sensitization and gold sensitization, respectively, are disclosed, for example, in U.S. Pat. Nos. 2,399,083 and 3,297,446.
Furthermore, it is known to increase the light sensitivity of silver halide emulsions by a combination of these sensitization methods, as described in T. H. James, The Theory of the Photographic Process, 4th Edition, pp. 149-160 (Macmillan Pub. Co., 1977).
In these conventional sensitization methods, as the amount of sensitizer is increased to obtain higher light sensitivity, the silver halide photographic emulsions tend to form fog, and it becomes difficult to control the formation of fog even by using antifoggants or stabilizers. Also, silver halide photographic emulsions sensitized by such conventional sensitization methods suffer from the disadvantage that when photographic films prepared by coating such silver halide emulsions are stored under high temperature and high humidity conditions, the photographic characteristics change greatly.
Attempts to improve the light sensitivity of silver halide emulsions by prolonging the chemical ripening period or increasing the ripening temperature are accompanied by an increase in the formation of fog, and it has been difficult to attain the desired purpose.
It is known to use a surface active agent having a betaine group as a coating aid for a photographic light-sensitive material, as described in U.S. Pat. No. 3,843,368. But such surface active agent does not have ability to increase the light sensitivity of silver halide emulsions.